Upgrade the pymongo dependency

Instead of requiring pymongo>=1.7, and failing hard with pymongo>=2.0,
upgrade the code to reflect some things moving from pymongo to bson,
and require pymongo>=1.9.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
Enable Travis-CI tests

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>